Dead Rising 2

Complete all case files with a co-op partner, saving and continuing from the co-op game where necessary. This can be done as your first playthrough, if you can find a dedicated partner.

NOTE: Some people have reported this trophy not unlocking for both players upon completing all case files. To reduce the possibility of this, either ensure that the host never continues with the game without having their co-op partner connected, or complete all case files in a single sitting.